Formation of Hydroxyapatite on Composites in CaO-P₂O₅-SiO₂-Al₂O₃ System by Hydrothermal Treatment

Abstract

Nine kinds of composite powders in CaO-P₂O₅-SiO₂-Al₂O₃ system were prepared by the sol-gel process. Although the as-prepared powders were amorphous, hydroxyapatite (HAp) and tricalcium phosphate (TCP) were formed as a calcium phosphate phase when they were heated from 800 to 1300°C. Additionally, anorthite (CaAl₂Si₂O₈) was formed in the composites containing 25mol% of Al₂O₃ and 25mol% of SiO₂ at 1100°C. The dense composite of 2.69g·cm^-3 bulk density was obtained by sintering powders with compositions of 38.48CaO⋅11.52P₂O₅⋅25SiO₂⋅25Al₂O₃ at 900°C for 5h. When this composite was hydrothermally treated at 160°C for 24h, β-TCP was changed into HAp to form a porous layer with the -8μm thickness on the surfaces of composites. The porous composite of 2.33g·cm^-3 bulk density was obtained when the powders with the compositions of 40CaO⋅10P₂O₅⋅10SiO₂⋅40Al₂O₃ were sintered at 1200°C for 5h. Ricelike HAp particles were formed on the surfaces and fracture surfaces of the porous composite treated hydrothermally at 160°C for 12h.